Sprint announced high-definition voice technology for the new HTC Evo 4G LTE smartphone and future phones, although HD Voice will only work once Sprint upgrades its 3G network, a process expected to begin in late 2012 in several cities.

HD Voice requires that both parties on a call use HD voice-capable smartphones on an HD voice-capable network, Sprint said in a footnote in a press release issued at the Evo 4G LTE unveiling Wednesday in New York.

Those conditions mean it could be years -- perhaps even a decade -- before significant numbers of users gain access to the improved voice quality, analysts said Thursday.

The feature requires that Sprint add HD voice capabilities to many other phones. To work well, other carriers in the U.S. would need to create network technology that interoperates with Sprint's as well as offer their own HD voice-enabled phones.

Though most cell phone users would like improved voice quality, it isn't their highest priority, said Kevin Burden, an analyst at ABI Research.

As a result, it's not clear that HD Voice will immediately be an important selling point for Sprint compared to other important features offered in the HTC Evo 4G LTE and other emerging smartphones, such as large, high-resolution screens, dual-core processors and long-lasting batteries.

"The public's expectation for voice quality on cell phones is so low right now that we're all willing to deal with [the way it is]. There's such a thing as 'good enough' technology. People look at voice quality today on cell phones and say, 'It's good enough; it sucks for me, but also for the guy on the other end,'" Burden said.

It wasn't always this way. In fact, Sprint used to tout its pure voice quality in 1980s advertisements. And Verizon Wireless became famous for its "Can you hear me now?" ads through the 2000s.

In recent years, though, mobile phone users have become used to nonverbal communications via text and email, partly because it doesn't take a lot of time and it's available when you want it.

"But some of the reason we use nonverbal communications over wireless is because we don't expect much out of the voice quality of our calls, and we know we won't catch all the words," Burden said.

Burden called HD voice a "noticeable" improvement over what's available on most cell phones today.

Visitors to Sprint's New York event on Wednesday were allowed to compare the voice quality of current Evo phones with that of the new EVO 4G LTE with HD Voice. Computerworld blogger Barbara Krasnoff called HD Voice a "vast improvement," at least in that controlled environments.

In marketing materials, Sprint describes HD Voice as "the next-generation evolution of voice quality and the future of voice communications for mobile phones. The service will provide fuller, more natural-sounding and less fatiguing voice quality and should reduce troublesome background noises often found in a cafe or on the street. Users should expect to identify voices and hear every word better that ever."

Sprint CEO Dan Hesse said that Sprint is the first U.S. carrier to announce plans for a nationwide HD Voice network. The HD network will be part of Sprint's Network Vision program, which also includes the 4G LTE upgrades. The new services will be launched mid-year in Atlanta, Baltimore, Dallas, Houston, Kansas City and San Antonio.

"When someone makes an important voice call, they can expect to find a clearer connection and a stronger signal in more areas," Sprint's press release said.

Sprint didn't say how many more of its phones will be getting HD Voice capability. A spokeswoman did say that Sprint plans to build the HD Voice specification "into additional devices in the future in order to build the ecosystem."

HD voice technology is defined by Webopedia as technology that provides "a deeper clarity and better audio experience" than conventional voice technology by doubling the sampling of voice communications that are digitized and transmitted and by more than doubling the breadth of the sound spectrum that's reproduced, ranging from 50 Hz to 7 KHz.